How fast? the rate of chemical change: notes and practice questions

Which species is an intermediate in the catalytic decomposition of ozone shown below?

Step 1: $Cl(g) + O_3(g) \rightarrow ClO(g) + O_2(g)$

Step 2: $ClO(g) + O_3(g) \rightarrow Cl(g) + 2O_2(g)$

A. $Cl(g)$

B. $ClO(g)$

C. $O_3(g)$

D. $O_2(g)$

The decomposition of dinitrogen pentoxide, $N_2O_5$, was studied at various temperatures to determine its activation energy. The following graph was obtained from the processed kinetic data, and the slope was calculated to be $-8500$.

Given the Arrhenius equation in its linear form: $\ln k = \frac{-E_a}{RT} + \ln A$.

Which expression gives the activation energy for this reaction?

A. $\frac{-8500 \times 1000}{R}$ $kJ$ $mol^{-1}$

B. $\frac{8500 \times R}{1000}$ $kJ$ $mol^{-1}$

C. $\frac{-8500 \times R}{1000}$ $kJ$ $mol^{-1}$

D. $\frac{8500 \times 1000}{R}$ $kJ$ $mol^{-1}$

The reaction between nitrogen monoxide and chlorine gas is shown below.

$2NO(g) + Cl_2(g) \rightarrow 2NOCl(g)$

The experimentally determined rate law is: $Rate = k[NO]^2[Cl_2]$.

What are the units for the rate constant, $k$?

A. $mol^2\ dm^{-6}\ s^{-1}$

B. $mol\ dm^{-3}\ s^{-1}$

C. $s^{-1}$

D. $mol^{-2}\ dm^6\ s^{-1}$

For a reaction that is second order overall, what are the units of the rate constant, $k$?

A. $\text{mol dm}^{-3} \text{s}^{-1}$

B. $\text{mol}^{-1} \text{dm}^{3} \text{s}^{-1}$

C. $\text{s}^{-1}$

D. $\text{mol}^{-2} \text{dm}^{6} \text{s}^{-1}$

A student investigates the kinetics of the reaction between hydrogen gas and iodine monochloride gas at a constant temperature. The reaction is represented by the equation:

$H_2(g) + 2ICl(g) \rightarrow I_2(g) + 2HCl(g)$

The following initial rate data were collected for the reaction:

What is the overall reaction order?

A. Zero order

B. First order

C. Second order

D. Third order

According to the Arrhenius equation, what is the relationship between the rate constant ($k$) and absolute temperature ($T$)?

A. $k$ is directly proportional to $T$.

B. $k$ increases exponentially as $T$ decreases.

C. A plot of $\ln(k)$ versus $1/T$ gives a straight line with a negative slope.

D. A plot of $k$ versus $T$ gives a straight line with a positive slope.

The dotted line in the graph below represents the volume of hydrogen gas evolved when excess solid zinc is added to $50.0\text{ cm}^3$ of $2.00\text{ mol dm}^{-3}$ hydrochloric acid.

Which curve (A, B, C, or D) represents the production of hydrogen gas when excess solid zinc is added to $100.0\text{ cm}^3$ of $0.500\text{ mol dm}^{-3}$ hydrochloric acid?

A. Curve A

B. Curve B

C. Curve C

D. Curve D

Which process has the smallest activation energy?

A. $N_2(g) \rightarrow 2N(g)$

B. $CH_4(g) \rightarrow CH_3(g) + H(g)$

C. $2CH_3(g) \rightarrow C_2H_6(g)$

D. $Na(g) \rightarrow Na^+(g) + e^-$

The gas-phase reaction between nitrogen monoxide and oxygen is believed to occur via the following two-step mechanism.

$2NO(g) \rightleftharpoons N_2O_2(g)$ fast

$N_2O_2(g) + O_2(g) \rightarrow 2NO_2(g)$ slow

Deduce the rate equation for the overall reaction.

A. Rate = $k[NO][O_2]$

B. Rate = $k[NO]^2$

C. Rate = $k[NO]^2[O_2]$

D. Rate = $k[N_2O_2][O_2]$

A substance is added to a reversible reaction which is observed to increase the rate at which equilibrium is attained. Which statement correctly describes the function of this substance?

A. It increases the average kinetic energy of the reactant particles.

B. It increases the value of the equilibrium constant, $K_c$.

C. It provides an alternative reaction pathway with a lower activation energy.

D. It is permanently consumed during the reaction.

The hydrolysis of 2-chloro-2-methylpropane, $(CH_3)_3CCl$, proceeds via a two-step $S_N1$ mechanism. The energy profile for this reaction is shown below.

Which statement correctly identifies the species at points P and Q?

A. P is an intermediate and Q is a transition state.

B. P is a transition state and Q is an intermediate.

C. P and Q are both transition states.

D. P and Q are both intermediates.

Which elementary reaction would be expected to have the largest value for the Arrhenius pre-exponential factor, A?

A. $Cl(g) + Cl(g) \rightarrow Cl_2(g)$

B. $NO(g) + O_3(g) \rightarrow NO_2(g) + O_2(g)$

C. $CH_3Cl(g) + F^-(g) \rightarrow CH_3F(g) + Cl^-(g)$

D. $2 NO_2(g) \rightarrow N_2O_4(g)$

The decomposition of a novel atmospheric pollutant, $X$, by reaction with an atmospheric radical, $Y$, was studied at a constant temperature. The following initial rate data were collected:

$\begin{array}{|c|c|c|c|}\hline\textbf{Experiment} & \textbf{[X] / mol dm}^{-3} & \textbf{[Y] / mol dm}^{-3} & \textbf{Initial Rate / mol dm}^{-3}\textbf{ s}^{-1} \\\hline1 & 0.100 & 0.100 & 2.00 \times 10^{-6} \\2 & 0.200 & 0.100 & 4.00 \times 10^{-6} \\3 & 0.100 & 0.200 & 8.00 \times 10^{-6} \\\hline\end{array}$

What is the overall order of the reaction?

A. 1

B. 2

C. 3

D. 4